epan/reedsolomon.h

   1 /** @file
   2  *
   3  * Global definitions for Reed-Solomon encoder/decoder,
   4  * by Phil Karn (karn@ka9q.ampr.org) September 1996
   5  * Copyright 1999 Phil Karn, KA9Q
   6  *
   7  * Wireshark - Network traffic analyzer
   8  * By Gerald Combs <gerald@wireshark.org>
   9  * Copyright 1998 Gerald Combs
  10  *
  11  * SPDX-License-Identifier: GPL-2.0-or-later
  12  */
  13
  14 #ifdef __cplusplus
  15 extern "C" {
  16 #endif
  17
  18 /* Set one of these to enable encoder/decoder debugging and error checking,
  19  * at the expense of speed */
  20 /* #undef DEBUG 1*/
  21 /* #undef DEBUG 2*/
  22 #undef DEBUG
  23
  24 /* To select the CCSDS standard (255,223) code, define CCSDS. This
  25  * implies standard values for MM, KK, B0 and PRIM.
  26  */
  27 /* #undef CCSDS 1*/
  28 #undef CCSDS
  29 #ifndef CCSDS
  30
  31 /* Otherwise, leave CCSDS undefined and set the parameters below:
  32  *
  33  * Set MM to be the size of each code symbol in bits. The Reed-Solomon
  34  * block size will then be NN = 2**M - 1 symbols. Supported values are
  35  * defined in rs.c.
  36  */
  37 #define MM 8 /* Symbol size in bits */
  38
  39 /*
  40  * Set KK to be the number of data symbols in each block, which must be
  41  * less than the block size. The code will then be able to correct up
  42  * to NN-KK erasures or (NN-KK)/2 errors, or combinations thereof with
  43  * each error counting as two erasures.
  44  */
  45 #define KK 207 /* Number of data symbols per block */
  46
  47 /* Set B0 to the first root of the generator polynomial, in alpha form, and
  48  * set PRIM to the power of alpha used to generate the roots of the
  49  * generator polynomial. The generator polynomial will then be
  50  * @**PRIM*B0, @**PRIM*(B0+1), @**PRIM*(B0+2)...@**PRIM*(B0+NN-KK)
  51  * where "@" represents a lower case alpha.
  52  */
  53 #define B0 1 /* First root of generator polynomial, alpha form */
  54 #define PRIM 1 /* power of alpha used to generate roots of generator poly */
  55 #define STANDARD_ORDER
  56
  57 /* If you want to select your own field generator polynomial, you'll have
  58  * to edit that in rs.c.
  59  */
  60
  61 #else /* CCSDS */
  62 /* Don't change these, they're CCSDS standard */
  63 #define MM 8
  64 #define KK 223
  65 #define B0 112
  66 #define PRIM 11
  67 #endif
  68
  69 #define NN ((1 << MM) - 1)
  70
  71 #if MM <= 8
  72 typedef unsigned char dtype;
  73 #else
  74 typedef unsigned int dtype;
  75 #endif
  76
  77 /* Reed-Solomon encoding
  78  * data[] is the input block, parity symbols are placed in bb[]
  79  * bb[] may lie past the end of the data, e.g., for (255,223):
  80  *      encode_rs(&data[0],&data[223]);
  81  */
  82 int encode_rs(dtype data[], dtype bb[]);
  83
  84 /* Reed-Solomon erasures-and-errors decoding
  85  * The received block goes into data[], and a list of zero-origin
  86  * erasure positions, if any, goes in eras_pos[] with a count in no_eras.
  87  *
  88  * The decoder corrects the symbols in place, if possible and returns
  89  * the number of corrected symbols. If the codeword is illegal or
  90  * uncorrectible, the data array is unchanged and -1 is returned
  91  */
  92 int eras_dec_rs(dtype data[], int eras_pos[], int no_eras);
  93
  94 #ifdef __cplusplus
  95 }
  96 #endif